Epidemiological studies indicate that reduced levels of HDL are an important risk factor for the development of atherosclerosis. A major theory to explain this relationship is that low levels of HDL are a metabolic marker for a tendency to accumulate atherogenic remnants of triglyceride-rich lipoproteins in plasma. The plasma cholesteryl ester transfer protein (CETP) mediates the transfer of CE from HDL to the triglyceride-rich lipoproteins. This pathway represents a major route for the catabolism of HDL CE in humans, and has the potential to increase the atherogenicity of remnant lipoproteins in subjects who accumulate these particles in plasma. The objective of this proposal is to understand on a molecular level the structure and function of plasma CETP and its role in HDL metabolism, as a means of furthering the understanding of the regulation and significance of HDL levels. The specific aims of the proposal are 1) to determine the three dimensional structure of CETP, by crystallization of the recombinant molecule; 2) to perform site-directed mutagenesis on the CETP molecule in order to elucidate amino acids that are necessary for lipid transfer or which mediate binding of CETP to specific lipoproteins; 3) to employ lipoprotein reconstitution and other techniques to define the molecular features of particular subclasses of HDL which permit specific recognition by CETP; 4) to use available CETP transgenic mice in order to determine in vivo the effects of hypertriglyceridemia and hepatic lipase on the expression of CETP activity; and 5) to examine the relationship between plasma CETP, lipoprotein levels and atherogenesis in an ongoing case-control study of the relationship of post-prandial lipoprotein changes to coronary artery atherosclerosis. The proposed studies will increase the understanding of the structure and mechanism of action of CETP, and will help to clarify the relationship between triglyceride-rich lipoproteins, HDL and coronary artery disease.